The present invention relates to an aqueous resinous composition consisting of an emulsion and a water-soluble polymeric material.
A mixture of an aqueous emulsion of acrylic or butadiene polymers and a water-soluble polymeric material such as polyvinyl alcohol or starch has been availably employed as a clear coating material for paper, binder for pigment coating, treating agent for fibrous materials, adhesive, tackifier, paint or molding material for fibers and films. In accordance with the mixing ratio, it is possible to improve a quality of the emulsion or the polymeric material. For instance, by adding polyvinyl alcohol to the emulsion, the flow property of the emulsion can be improved and it becomes possible to obtain the flow property required in application such as coating or molding. In the case of polyvinyl alcohol, by adding the emulsion to polyvinyl alcohol, it becomes possible to raise the sizing effect to paper or fibrous materials, to give a water-resistant property, to improve the strength of molded article or to control the flexibility of molded article. An aqueous emulsion of acrylic or butadiene polymers has been generally prepared by subjecting monomers to emulsion polymerization in the presence of an emulsifier and an initiator in an aqueous medium, and it has been known that the emulsifier used in the polymerization has a great influence on the properties of the resulting emulsion. As the emulsifier, nonionic or anionic surface active agents have been usually employed, and in some cases, in combination with polyvinyl alcohol as a protective colloid.
However, according to the investigation of the present inventors, it has been found that the mixture of the emulsion prepared in the presence of such an emulsifier and the water-soluble polymeric material has the disadvantages of poor storage property, especially at a high temperature, due to poor miscibility between the emulsion and the polymeric material, and of large dependence on shearing rate. The poor storage property increases the viscosity with the lapse of time and finally causes gelation or separation into layers and, therefore, it is impossible to storage the mixture for a long period of time. The large dependence on shearing rate makes it difficult to uniformly coat the mixture on surfaces of paper and, therefore, the coating requires severe process control. Also, the large dependence on shearing rate causes troubles in preparing molded articles from the mixture because the shape or construction of molded article is largely varied by a slight changing of a molding speed at a nozzle or slit of a molding machine. Thus, the known mixtures are not necessarily satisfactory.